Spandex

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Introduction to Spandex (Chapter 1) Chapter 1: Production Methods and Uses of Spandex 1. Spandex Elastic Fiber Spandex, also known as \"Spandeks\", is an elastic fiber; its scientific name is polyurethane fiber, abbreviated as \"PU\". Mainland China calls it “spandex”. It is highly elastic, capable of stretching 6 to 7 times its original length, but it can quickly return to its initial state once the tension is removed. Its molecular structure is a chain-like, soft, and elastic polyurethane, whose properties are enhanced by being connected to hard segments. Elastic fibers are divided into two categories: those with polyester chains and those with polyether chains. Polyester elastic fibers have strong antioxidant and oil-resistant properties ； Polyether elastic fibers have good mildew resistance and are resistant to detergents. II. Development of Spandex Since DUPONT introduced Spandex for commercial use in 1958 and registered it as the trademark “LYCRA”, which is transliterated in the market as “Layka”, many people have come to use “Layka” as a synonym for Spandex. Subsequently, production took place around the world. Examples include “VYRENE” from U.S.RUBBER CO. in the United States, “ESPA” from TOYOBO in Japan, “DORLASTAN” from BAYER, A.G., W.GERMANY in Germany, “SPANZELLE” from COURTAULDS, U.K., “ESTANE” from B.F.GOODRICH CHEMICAL CO., LTD, “FUJIBO” from Fuji Spinning in Japan, “TORAY-DUPONT” developed through a partnership between DUPONT and Toray in Japan, “CLEARSPAN” and “GLOSPAN” from GLOBE MANUFACTURING CO. in the United States, “ACELAN” from TAE-KWANG in South Korea, “TEXLON” from Tongkook, “TOPLON” and “CREORA” from HYOSUNG, which is the largest producer in the world. There is also “ROICA” from Asahi in Japan; in early 1999, Asahi partnered with Formosa Plastics Group in Taiwan to establish the company FORMOSA ASAHI, abbreviated as FAS. MOBILON from Nisshin Spinning in Japan also set up production lines in Taiwan to manufacture TOWNSPAN fiber. In Taiwan, SHEIFLEX was produced by Xue Yongxing’s company. On the Chinese mainland, companies such as Newstar in Yantai and Aoshen in Lianyungang use the equipment and technology of TOYOBO for production. The spandex factory in Heshan, Guangdong, began operations in 1996, and production of spandex also started in Changle, Fujian, Haimen, Nantong, and Zibo, Shandong. In China, DUPONT collaborates with Huayuan in Shanghai to produce spandex, while Zhejiang Huafeng’s “Millennium” brand of spandex was put into production in 2000. Additionally, DUPONT also collaborates with other manufacturers (though it is not involved in the production process) to sell under the “ELASPAN” brand. Investments are being made or production of spandex is being expanded around the world, driving strong growth in the elastic fiber market. III. Spandex production methods: Depending on the spinning method, the processes used for producing spandex can be divided into solution spinning, melt spinning, and chemical reaction spinning. Solution spinning is further divided into dry solution spinning and wet solution spinning, depending on the solidifying medium used. Currently, dry spinning accounts for over 80% of global spandex production worldwide, wet spinning accounts for about 10%, while the other two methods together account for roughly 10%. And to date, there is no chemical reaction method in our country. Due to issues such as complex processing, low spinning speed, high production costs, large equipment investment, and environmental pollution caused by diamines, the chemical reaction spinning method has little potential for further development in the future. Spandex fibers overcome quality defects such as stress and strain properties, the range of deniers, and the moldability of rubber yarns; DUPONT was the first to use dry spinning for their production back in those days. To this day, there are roughly four production methods: 1. Dry spinning: A method in which the solution solidifies into filaments as the solvent evaporates under hot air flow. In dry spinning, polyether diol and diisocyanate are combined in a molar ratio of 1:2 to form a prepolymer under specific reaction temperature and time conditions. After the prepolymer is dissolved by adding a solvent, diamine is introduced to carry out a chain extension reaction, resulting in a block copolymer solution. Further processes such as mixing, filtering, and degassing are then employed to produce spinning dope with uniform properties. Then it is pressurized into the spinning head in a precise and uniform manner using a metering pump. Under pressure, the spinning solution is extruded from the capillaries of the spinneret to form a fine thread stream, which then enters the channel. The tunnel is filled with hot air, which causes the solvent in the filament stream to evaporate rapidly and be carried away by the air. The concentration of the filaments continues to increase until they solidify. Meanwhile, the filament stream is stretched and thinned, and finally wound into a certain package. Production process: Solution ---- Spinning pump (filtration) ---- Drying oven (heated air at 100°C to evaporate the solution) ---- Spinning ---- Winding and shaping. Spinning speed: 200–800 M/min. Spinning temperature: 200–230°C. Fiber fineness: 1.1–1244 dtex. Materials used: DUPONT, Bayer, Toyobo, Hyosung. Characteristics: High level of pollution during the process, complex manufacturing process, high costs. 2. Melt-spinning: A method in which polymers are heated above their melting point to become a melt, which is then used to form fibers. Melt spinning involves feeding the dried thermoplastic polyurethane chips into a screw extruder; the chips melt due to the heat, and the melt is extruded under certain pressure and delivered to the spinning area. Then, a spinning pump is used to press the melt in a precise and uniform manner into the spinning components. A molten filament is extruded from the holes in the spinneret and cooled in the channel to solidify into fibers. Melt spinning is only applicable to polyurethane block copolymers that are easy to melt and have good stability at their melting temperature, with a spinning speed of 200–800 m/min. 　　The melt spinning process has a short production cycle, requires low investment, does not need solvent recovery, and results in low costs. However, the melt-spun spandex technology is not yet mature; production costs and product quality are greatly affected by raw materials, and the production of raw material chips is subject to external control. Moreover, due to differences in spinning processes and raw materials, dry-spun spandex and melt-spun spandex exhibit certain differences in structure and properties. Dry-spun spandex has superior performance, whereas in the case of melt-spun spandex, the instability of the prepolymer at processing temperatures leads to excessive cross-linking when it is exposed to high temperatures for an extended period, resulting in the formation of gels. This results in lower physical and mechanical properties of the final product, a lower quality grade, and a narrower range of applications. At present, the scale of spunbonded spandex production facilities in our country is relatively small, with low production capacity as well. Production process: Polymerization of the polymer without the use of solvents — granulation — slicing at a constant temperature — cleaning to remove impurities — drying — dehydration — feeding into a screw press to form a melt — extrusion through a spinneret — cooling in a cold box — winding into shape. Spinning speed: 600–1600 M/min. Spinning temperature: 160–220°C. Fiber fineness: 9–1100 dtex. Manufacturers used: bell spin, Bayer, Nisshin Spinning. Features: short production process, low cost, minimal pollution. 3. Wet spinning: A method in which the solution is solidified into fibers through double diffusion in a coagulation bath. Similar to dry spinning, wet spinning also creates a block copolymer solution, which is pumped into the spinneret via a metering pump. The fine stream of the raw material extruded from the capillaries of the spinneret enters the coagulation bath; the solvent in this stream diffuses into the coagulation bath, causing the concentration of polymer to increase. Fibers are then formed within the coagulation bath, and after washing and drying, they are wound up. Compared to wet spinning, dry spinning results in a higher concentration of polymer and higher viscosity; it can withstand a greater drawing ratio for the spinneret, and the fibers produced are finer than those obtained by wet spinning. At the same time, dry spinning uses hot air as the solidification medium; compared to a solidification bath, it results in less fluid dynamic resistance for the filaments during the spinning process, higher spinning speeds, and greater production volumes. Wet spinning has been gradually phased out due to high production costs. The only two wet spinning units in our country have ceased operation. Production process: Mother liquor ---- Spinning pump (filtration) ---- Entering warm water (below 90°C) from the spinneret ---- Coagulation bath in the regeneration tank ---- Removal of solvent ---- Filament washing ---- Drying ---- Winding and shaping. Spinning speed: 50–150 M/min. Spinning temperature: warm water below 90°C. Fiber fineness: 44–440 dtex. Manufacturer: Fuji Spinning, Japan. Characteristics: This production method results in high pollution, slow spinning speed, and high costs. 4. Chemical reaction method: A method in which polymers are converted into a solution, and a chain-extending agent is used to trigger a chemical reaction, thereby curing them into fibers. Production process: Solution ---- through the spinneret to the solidifying liquid ---- addition of chain extender (chemical reaction) ---- winding into shape ---- hardening ---- processing into network fibers. Spinning speed: 50–150 M/min. Fiber fineness: 44–80 dtex. Manufacturer: Universal USA. Characteristics: This production method results in high pollution and high costs. 5. Introduction to the main manufacturing processes 1) Invista and Hyosung technologies: Invista (formerly DuPont) was the first to achieve industrialization of dry-spinning for spandex; its spandex product, Lycra, stands out in terms of product quality and brand promotion. NVIDIA and Hyosung’s technologies utilize continuous polymerization and high-speed spinning, resulting in better product quality compared to conventional batch polymerization and medium-speed spinning. At the same time, it features high yield, low consumption of utility resources, and low unit production costs. However, the technical barriers to spandex production are extremely high. Invista and Hyosung’s development strategies in China primarily involve setting up joint ventures; no technology transfer takes place. As a result, Chinese spandex manufacturers basically rely on Japanese technology. 2) Toyobo Technology: Toyobo was one of the first companies in Japan to produce spandex and fibers. In 1963, it developed its own proprietary dry-process production technology, utilizing a process that combines batch polymerization with continuous spinning. Through years of refinement and improvement, this process has become mature and the production process is stable. The spinning speed is 500–600 m/min; based on this, some domestic enterprises have achieved a spinning speed of up to 800 m/min through technological upgrades. The products feature excellent performance and a full range of specifications, from 20D to 210D. They have a wide range of applications and can be used in weaving, tricot, warp knitting, sock manufacturing, core spun yarns, covered yarns, and more. In terms of solvents, Toyobo’s new technology uses the environmentally friendly solvent DMAC as a replacement for DMF, **reducing environmental pollution. Some of China’s major spandex manufacturers, such as Yantai Spandex, Zhejiang Huafeng, Lianyungang Du Zhong, Jiangsu Shuangliang, and Hangzhou Shuerzi, all utilize Toyobo’s technology. 3) Nisshin Spinning Technology: Nisshin Spinning also employs batch polymerization and continuous spinning processes, with a spinning speed of 600–800 m/min. Its technology is relatively advanced in terms of developing fine-denier fibers and enhancing the elasticity and stretch of products; some newly established enterprises such as Longshan in Shaoxing, Zhejiang, and the fourth phase of Shuangliang in Jiangsu use this technology. In recent years, China’s spandex technology has seen significant improvement; continuous enhancements have been made on the basis of technological imports, the production processes have become more mature and stable, spinning speeds have increased, and costs have gradually decreased. Some companies have essentially achieved localization of their production technologies. As production technologies advance rapidly, the application technologies for spandex have also developed swiftly. New processes and techniques for spandex products continue to emerge, enabling further expansion of the spandex market. At present, China already possesses strong market competitiveness in conventional spandex products, but it still lags significantly behind countries such as the United States and Japan in terms of differentiated and functional products. With a significant decline in investments in spandex and a rapid increase in production capacity, market competition has intensified. Therefore, developing advanced productive forces and promoting industrial upgrading through technological progress will be the main tasks for the spandex industry in the future. IV. Forms of Spandex: In Spandex production, different levels of luster are available. Taking DUPONT as an example, the common forms include: CLEAR-LUSTER: The fibers on the surface are relatively smooth, which results in a transparent reflection; it has a low friction coefficient, poor uniformity in fiber thickness, and limited color retention. It is suitable for use in combination with short-fiber materials and is often used in woven fabrics. Dull-Luster: Also known as plain white, it features a rougher surface texture with a larger friction area, resulting in good coloring effects. It is suitable for use in products made from long fibers, and is often used for coarse-count yarns, such as in items for the chest area and various accessories. Semi-transparent (BRIGHT-LUSTER): Titanium dioxide and anti-slip agents are added to it. It has strong resistance to chemicals and is often used in swimwear due to its chlorine resistance. Matte finish (MATT-LUSTER): It lies between pure white and translucent, presenting a matte white color that is suitable for use in knitting. Spandex has various uses and comes in different product forms, mainly divided into three types: bare yarn, core-spun yarn, and covered or twisted yarn. Each different combination corresponds to a different use. Bare yarn: It is 100% spandex yarn. Bare yarn is generally not used directly in fabrics; it is usually produced together with other materials, and special equipment is required for its production. Knitwear is the most commonly used, such as swimsuits and sportswear, and generally ranges from 22 to 78 Dtex. Core spun yarn: A yarn in which bare yarn serves as the core and other materials form the outer sheath; abbreviated as CSY. In the case of cotton core yarns, where drawn bare yarn is inserted into the spinning frame of a ring spinner, the elongation of the bare yarn wrapping around the core yarn must be appropriately adjusted; its stretch ratio is kept within 2 to 3 times. Today, core spun yarns are divided into hard-core yarns and soft-core yarns, with cotton, polyester, acrylic, and others serving as the competing materials for core spun yarns. It is widely used in fabrics, knitted goods, bandages, socks, underwear, and denim; the denier value is usually between 22 and 235 Dtex. Typical count and blending percentage (%) of covered yarns: 60s cotton covered with 22 dtex = 92% cotton, 8% spandex; 80s cotton covered with 22 dtex = 90% cotton, 10% spandex; 55s cotton covered with 33 dtex = 91% cotton, 9% spandex; 60s cotton covered with 33 dtex = 90% cotton, 10% spandex; 30s cotton covered with 44 dtex = 92% cotton, 8% spandex; 40s cotton covered with 44 dtex = 90% cotton, 10% spandex; 50s cotton covered with 44 dtex = 87% cotton, 13% spandex; 12s cotton covered with 78 dtex = 96% cotton, 4% spandex; 16s cotton covered with 78 dtex = 95% cotton, 5% spandex; 20s cotton covered with 78 dtex = 93% cotton, 7% spandex; 30s cotton covered with 78 dtex = 90% cotton, 10% spandex; 40s cotton covered with 78 dtex = 87% cotton, 13% spandex; 50s cotton covered with 78 dtex = 84% cotton, 16% spandex; 20s cotton covered with 122 dtex = 93% cotton, 7% spandex; 36s cotton covered with 122 dtex = 91% cotton, 9% spandex; 8s cotton covered with 155 dtex = 95% cotton, 5% spandex; 20s cotton covered with 155 dtex = 88% cotton, 12% spandex; 36s cotton covered with 155 dtex = 79% cotton, 21% spandex; 40s cotton covered with 155 dtex = 77% cotton, 23% spandex. For coated or twisted yarns: long fibers such as nylon and polyester are used in the production of elastic fabrics; these coated or twisted yarns are combined with plain yarns to create such fabrics. Often, in order to increase the degree of coverage by spandex, two or three plain yarns may be used together. When one plain yarn is coated, it is called single-coated yarn (SCY); when two plain yarns are coated, it is called double-coated yarn (DCY). Thicker versions are referred to as FTY. The typical denier range for these yarns is 44–620 dtex, and they are used in underwear and related accessories. General mixing ratio of denier levels for coated and twisted yarns (%): 56 dtex nylon coated with 78 dtex = 88% nylon, 12% spandex; 78 dtex nylon coated with 78 dtex = 92% nylon, 8% spandex; 78 dtex nylon coated with 33 dtex = 88% nylon, 12% spandex; 78 dtex nylon coated with 44 dtex = 63% nylon, 14% spandex; 78 dtex nylon coated with 78 dtex = 78% nylon, 22% spandex; 83 dtex nylon coated with 22 dtex = 92% nylon, 8% spandex; 83 dtex nylon coated with 33 dtex = 89% nylon, 11% spandex; 83 dtex nylon coated with 44 dtex = 86% nylon, 14% spandex; 83 dtex nylon coated with 78 dtex = 78% nylon, 22%. Special fiber mixing ratios (%): 20s/2 cotton coated with 44 dtex = 98% cotton, 2% spandex; 30s/2 cotton coated with 44 dtex = 97% cotton, 3% spandex; 40s/2 cotton coated with 44 dtex = 96% cotton, 4% spandex; 20s/2 cotton coated with 78 dtex = 96% cotton, 4% spandex; 30s/2 cotton coated with 78 dtex = 95% cotton, 5% spandex; 40s/2 cotton coated with 78 dtex = 93% cotton, 7% spandex; 30s/2 polyester coated with 44 dtex = 97% polyester, 3% spandex. Chapter 2: Comparison of Spandex Production Processes. Based on the characteristics of the spinning processes, the current spandex production methods include solution dry spinning, solution wet spinning, reactive spinning, and melt spinning. The following compares the technical and product characteristics of several processes: 1. Solvent-free method: Polyether diol and diisocyanate are combined in a molar ratio of 1:2 under specific reaction temperature and time conditions to form a prepolymer. After the prepolymer is dissolved in a solvent, diamine is added to carry out a chain-extension reaction, resulting in a block copolymer solution. Subsequent steps such as adding additives, mixing, filtering, and degassing are then performed to produce spinning dope with uniform properties. It is then pressed in quantitatively and evenly into the spinneret using a metering pump; the spinning solution is extruded from the capillaries of the spinneret plate to form fine filaments, which enter the spinning channel. The passage is filled with hot air (or hot nitrogen), which causes the solvent in the filament stream to evaporate rapidly and be carried away by the air (or nitrogen). The concentration of the filaments continues to increase until they solidify. Meanwhile, spandex is typically produced as multifilaments; before solidification, a twister is used to twist them together. Finally, the filaments are oiled and wound onto bobbins to form specified packages. Dry spinning is currently the most widely used spinning method for spandex in the world. Dry spinning accounts for about 80% of the world’s total spandex production. Its fineness ranges from 1.1 to 123 tex, with the spinning speed generally being between 200 and 600 m/min; in some cases it can even reach up to 1200 m/min. The dry spinning process is well-developed, resulting in fibers of excellent quality and performance. DuPont, Bayer, Toyobo, and most domestic manufacturers all use the solution dry spinning technique. 2. Solution wet method: First, a block copolymer solution is prepared by using polyester diols and diisocyanates in a manner similar to dry spinning. After pre-treatment, the solution is sent to the spinning machine and pumped into the spinneret through a metering pump. The fine stream of the dope extruded from the capillaries of the spinneret enters the coagulation bath. The coagulation bath uses warm water (below 90°C) as the coagulating medium; the solvent from the solution stream diffuses into the coagulation bath, causing the concentration of polymers in the solution stream to increase gradually, thus forming fibers. These fibers are then washed, dried, and wound up. The wet spinning speed is generally 5–50 m/min, with a fineness of 0.55–7.7 dtex. The wet spinning process has a complex workflow, high investment costs for equipment, a low spinning speed, and high production costs. This method has been gradually phased out. Currently, the output from wet spinning accounts for about 10% of the total spandex production. 3. Reaction method: The reaction spinning method, also known as chemical spinning, involves a chemical reaction or the use of chemical reactions to control the fiber formation rate when transforming the spinning solution into solid fibers. In reactive spinning, the reaction process by which monomers or prepolymers form polymers occurs simultaneously with the fiber-forming process. A polyether or polyester prepolymer solution with diisocyanate groups at both ends is forced out through a spinneret into a curing bath, where it reacts with the chain extenders in the bath to form primary fibers. After being wound, the nascent fibers should also be hardened in pressurized water, so that the unreacted parts within the fibers can be cross-linked, thereby transforming them into polyurethane block copolymers with a three-dimensional structure. The spinning speed in the reactive spinning method is generally 50–150 m/min, with a fineness of 0.56–38 tex. Due to issues such as complex manufacturing processes, low spinning speeds, high production costs, and large equipment investments, this method has gradually been phased out. Currently, the output of reactive spinning worldwide accounts for about 10% of the total spandex production. 4. Melting method: The melting spinning method is a technique for fiber formation using the molten fluid of polymers. Melt spinning can only be applied to polyurethane block copolymers with good thermal stability, such as those obtained by the polycondensation of 4,4’-methylenediphenyldiisocyanate and 1,4-butanediol. The spinning temperature ranges from 160 to 220°C, and the spinning speed is generally between 200 and 800 m/min. The melt spinning of spandex is mainly completed through 6 steps: sheet drying → melting → formation of melt filaments → cooling → drawing → winding. Since some macromolecules degrade during high-temperature extrusion, a certain amount of crosslinking agent must also be added to the extrusion equipment to reconnect the molecular chains containing active -NCO end groups. Due to the process characteristics of melt spinning, the products obtained can achieve a high elongation at break; however, because the intermolecular forces are lower compared to those of products produced by other methods, the restoring force is weak and the elastic recovery is poor. Therefore, melt-spun spandex yarn can only be used in applications with lower requirements, such as socks, and its adoption is limited due to the high price of spandex chips. However, we should also recognize the advantages of melt-spun spandex fibers in terms of investment costs and environmental impact; if the drawback of poor elastic recovery can be addressed, they will undoubtedly possess high competitiveness. In fact, in recent years, foreign companies such as Zhongfang have gained a significant advantage in melt-spun spandex by improving crosslinking agents, and in some aspects they can now compete with dry-spun spandex. Therefore, while vigorously developing dry spinning, domestic manufacturers should continue to increase investment in research and development related to melt spinning in order to stay at the forefront of international spandex technology development. Chapter 3: Molecular Structure of Spandex Spandex (polyurethane fiber) is a block copolymer, whose long molecular chains are typically composed of alternating soft segments formed by polyurethane bonds and hard segments formed by urea bonds (the structure of spandex produced by melt spinning differs due to its different synthesis process). Its number average molecular weight is generally above 25,000. The soft segments are in a curled, amorphous state; the molecules can slide past one another and can be stretched under tension. The rigid segments form hydrogen bonds with each other, resulting in a state similar to that of a crystal, acting as binding points. It is precisely due to this unique molecular structure that spandex not only possesses high elasticity but also excellent recovery properties after being stretched. The left image is a schematic diagram of the molecular structure of spandex. Chapter 4: Properties of Spandex. Spandex is generally composed of multiple filaments, typically 10D per filament; nowadays, there are also filaments with a diameter of 15D or even 20D per filament. The fewer the theoretical roots, the better the uniformity of the filaments, as there are fewer chances of overlapping patterns. The production solution DMAC used in dry spinning is harmful to the human liver; generally, its concentration is controlled at 0.5 mg/kg per 10D root, while it is 0.7 mg/kg per 15D root, which exceeds the standard limit. When producing Spandex, special attention must be paid to factors such as winding tension, yarn count on the drum, breaking strength, elongation at break, shape retention, oil adhesion, and elastic recovery rate. These issues have a direct impact on weaving, and extra care is required especially when producing single-sided fabrics through knitting. I. Physical Properties 1. Packaging draft (%): The drafting tension on elastic fibers is very important; this tension must remain uniform from the inside to the outside. If the tension is not uniform, it will directly affect the quality of the woven fabric. The optimal drafting tension is 8%-12%. And the tension error of each bobbin must not exceed 3%. 2. Dtex on cheese: The dtex value on the drum is determined by the winding tension; for example, if the winding tension is 10% for 44 dtex, then the actual dtex value on the drum is 40 dtex, which means it is 10% finer. Currently, some spandex manufacturers believe that when the weight per unit of spandex is the same for each brand, spandex with higher winding tension undoubtedly has a greater length and more weaving length, allowing the fabric to be made lighter; it is therefore necessary to consider the requirements of one’s own products when making a choice. 3. Breaking Tensile Strength: Generally, spandex of different brands or series exhibits varying strength levels. The testing method involves using a tensile testing machine to test samples of 50 mm in a controlled environment, at 100% (SS100), 200% (SS200), and 300% stress levels, with five tests conducted for each level. Typically, the data for 200% (SS200) as well as the stability of the other data points are examined; the higher the strength, the greater the stretching capacity of the fabric, allowing for faster weaving speeds. 4. Breaking Elongation: When measuring the breaking strength, it is possible to determine the amount of elongation that occurs at the point of breakage; generally, the greater the elongation, the lower the proportion of fabric components in the material. 5. Shape: Judged by visual inspection; any defects such as poor shaping, uneven shapes of individual tubes, or variations in size result in rejection. 6. Oil adhesion: The oil content in spandex should ideally be 5% (+/-2%). The higher the oil content or the longer the exposure time, the more oil from the outer layer penetrates into the inner layers, accumulating at the bottom of the tube, which affects the weaving tension and leads to increased wear and tear. The general oil component is silicone oil, containing metal stearate ions. 7. Elastic recovery rate: Fibers that can be stretched by 100% or more are considered elastic fibers. These fibers increase in length under tension, and when the tension is removed, they return to their original length. The ratio of the original length to the recovered length is the elastic recovery rate, which is generally 95% or higher. 8. Specific gravity: The specific gravity of spandex is 1.10. 9. Standard moisture content: generally 1.3 (ASTM). 10. Softening temperature: generally 190 degrees Celsius/390 degrees Fahrenheit. 11. Melting temperature: generally 250 degrees Celsius/437 degrees Fahrenheit. II. Standard methods for storing and using Spandex: Spandex should be stored in an environment with constant temperature and humidity, at a temperature of 18-20 degrees Celsius; the lower the temperature, the longer the storage period will be. The relative humidity should be between 60%-70%. It should not be placed in areas exposed to direct sunlight, nor should it be stored together with chemical substances such as sulfur dioxide and nitrogen oxides, as this can cause it to decompose. Storage period: 20D and below (3 months), 30D (4 months), 40D–70D (6 months), 100D–280D (9 months), 420D and above (12 months); the thicker the Spandex, the longer the storage period. When using Spandex in weaving, the cardboard boxes are opened at least 16 hours in advance, transferring them from the temperature-controlled warehouse to the weaving workshop, where they are allowed to absorb moisture, in order to reduce yarn breaks during weaving. III. Simple testing methods for Spandex 1. Boiling water shrinkage test 1) Take four spandex samples, remove the surface layer, then cut three sections of 10 cm each and mark the distances with a colored pen. 2) Place the sample in boiling water (100°C) for 10 minutes, then remove it and let it air-dry at room temperature; measure its shortened length after 5 minutes. 3) Calculate its boiling shrinkage rate based on the difference before and after boiling, with a standard range of 10–15%. Boiling water shrinkage (%) = (10 cm – test length) / 10 × 100%. Conclusion: A boiling water shrinkage exceeding (10–15%) indicates poor stability of the spandex. 2. Spandex elasticity test: 1) Take four spandex samples, remove the surface layer, then cut three sections of 10 cm each, and mark the distances with a colored pen. 2) Join the ends of the sample and place it on a single yarn strength tester for testing, with stretching at a speed of 50 cm/minute. 3) First, the sample is stretched by 100%, 150%, 200%, 250%, and 300% respectively, three times each, and then its tensile stress (cn) and elastic recovery rate are calculated for the fourth time. Elastic recovery rate % = (10 cm – test length) / 10 × 100%. Conclusion: Different products have varying requirements regarding the elasticity of spandex; some require low elongation and high elasticity, while others require high elongation and low elasticity, or low elongation and high elasticity, or high elongation and low elasticity. Therefore, different types of fabrics require appropriate spandex types. Compared with other brands at a rate of 300%, the standard rate ensures consistent quality of spandex used by enterprises. IV. Various functional categories of spandex: The conventional spandex from each brand comes in different levels of stretch and strength. By selecting the appropriate spandex based on the requirements of the final product, it is possible to produce elastic fabrics that meet the desired specifications. In addition to regular spandex, various brands have recently developed spandex products with special functions, providing users with more options that better meet the requirements of end products. For example: 1. Special elastic comfort feature: DUPONT’s LYCAR-SOFT is the top choice; its advantage is that the fabric does not feel tight when worn. DUPONT imposes strict requirements on LYCRA-SOFT fabrics, issuing a certification only after they meet these standards. Typically, the fabric is tested using an INSTRON tensile tester for its stretching and recovery properties, with the following criteria for success: 1) For warp-knitted fabrics: A MINIMUM 70% WORK RECOVERY SLOPE of 5.0 OR LESS; 2) For weft-knitted fabrics: A MINIMUM 70% WORK RECOVERY SLOPE of 10.0 OR LESS. Asahi Kasei’ s ROICA HS series also offers similar capabilities. 2. Special chlorine resistance: such as ROICA-SP from Asahi Kasei, T-162 from DUPONT, ESPA T-365 from TOYOBO, MOBILON-K from NISSHINBO, CREORA C-200 from HYOSUNG, etc. 3. Special high-temperature resistance feature: Suitable for synthetic fibers such as DUPONT’s T-169, TOYOBO’s ESPA T-765, NISSHINBO’s MOBILON-P, and HYOSUNG’s CREORA C-300, etc. 4. Special low-temperature function: Suitable for fabrics whose materials are not resistant to high temperatures, such as wool, nylon, or colored fabrics that may change color or turn yellow due to bleaching when exposed to high temperatures; examples include TOYOBO’s ESPA-M, NISSHINBO’s MOBILON-R, and FUJIBO’s U-type products. 5. Special moisture absorption and vapor permeability functions: such as RIOCA-BZ from Asahi Kasei, and the EM series from FUJIBO. 6. Durability and wear resistance features: such as TOYOBO’s ESPA T-70, FUJIBO’s Type E, etc. 7. Other special functions: such as the antibacterial and deodorizing features of FUJIBO’s KA and UA models, as well as far-infrared radiation from the EF model, and so on